This invention relates to plastic parts provided with a surface-hardening coating film containing an ultraviolet absorber. A typical example of such plastic parts is a plastic lens for automobile headlamps.
Many kinds of plastic parts for automobiles, buildings, audio and video appliances, etc. are provided with a surface-protecting or surface-hardening coating film. In many cases nonmetallic polymers are used for the coating purpose, and in such cases it is usual to produce a two-layer coating film consisting of a primer layer and a top-coat layer that is a hard-coat layer. For coating plastic parts that are required to possess transparency, such as plastic lenses, it is prevailing to use an acrylic resin base or silicone base hard-coat material with a view to enhancing scratch resistance of the coating film. It is often, and it is usual where the coated plastic parts are for outdoor uses, to add an organic compound that serves as an ultraviolet absorber to the hard-coat material.
By testing with a sunshine weather-O-meter, durabilities of conventional surface-hardening coatings on plastic parts rarely exceed the level of 2000 hr. For most of plastic parts for automobiles the 2000 hr level of durability can be taken as assurance of sufficient practicability. However, further durability or weatherability is required of some exterior parts which must long retain transparency such as windows and lenses for headlamps. It is conceivable to increase the content of the ultraviolet absorber in the hard-coat layer of the surface-hardening coating, but this measure causes lowering of the surface hardness of the coating.